Considerably less thought out and described than normal, owing to triviality. Fact checks are welcome as I have performed almost none.
That being said, whilst I was finding some more instances of the Godfrey Spiral, I noted that there were green gems on the Cleanrot Spear, specifically under the spearhead, and generally imperceptible in gameplay because of their size and position relative to the normal camera:
On the wiki, with the item laid out, these gems can be perceived:
I'm fairly certain this was noted near the game's release, but got overshadowed by more important lore.
Whether these are simply green gems, green amber, or green glintstone is unconfirmed.
However, green amber doesn't seem to have a strong connection to Malenia/Miquella, unlike the Haligtree's orangey-yellow amber, and also seems quite wasteful; presumably Godwyn's especially special knights got tiny little talismans of amber, so it seems a bit out of wack that Miquella was pumping out gallons of sap from his storerooms for his regular knights.
Them being green gems is possible, and cannot really by refuted by claims of uselessness, as a great number of weapons in this game are styled with seemingly useless adornments and gems.
That being said, these gems aren't exactly presented out and about on the weapon, and seem as if they are instead being shielded by the base of the spear head; they aren't really visible to an enemy getting stabbed, so I lean towards them perhaps having some actual function, and necessarily needing to be protected under metal.
Indeed, one can make a more flavorful reading were these indeed green glintstone.
These 4 posts seem relevant and can help frame some ideas: (1) (2) (3) (4)
Namely, green glintstone appears as if it may have a connection to poison or poisonstones (green in general to rusting and rot with verdigris), and also appears to be quite connected to Rykard, both in usage and in potential sources.
Besides the usage of green gems in the serpent-people's weaponry (Magma Whip Candlestick), and, again, the potential establishment of "green-poison" glintstones being connected to the serpent-people's (and Rykard's) poison breath attacks, green glintstone purportedly appears being mined in 2 areas, the Ruin-Strewn Precipice and the Sealed Tunnel, that I believe intimately connected to the Volcano Manor.
The former is referred to by Rya almost as if knowledge of the mine's creation was not particularly widespread:
At the base of the valley near the Grand Lift, there's an old tunnel.
It was excavated from both ends, linking Liurnia to the Altus Plateau.
I have faith in you, A champion, through and throught.
It is also, by the Finger Reader at the East Raya Lucaria Gate, presented as if it is something hidden to find:
Without even the half crescents that wish to be whole.
Before the unmoving, unfeeling Grand Lift ahead.
…
Or, are you planning to throw yourself to the waters?
To find the coward's passage, through the dim cavern?"
Namely, the coward's path appears hidden, but Rya knows of it. Obviously her goal is to send a champion to Tanith, but the point is simply the Manor's knowledge of a green-glintstone producing mine.
Next, the Sealed Tunnel is the path to Rykard's Divine Tower, that of West Altus. It holds an Abuctor Virgin, among other enemies. And, of course, the "sealed" namesake refers to illusory walls which can be broken, just as those used in the Manor itself.
Thus, there are two locations with green glintstone, both of which appear overviewed by Rykard's forces.
And yet, the location in the base game most highly associated with poison and its usage is the Shaded Castle, which bears its allegiance to Malenia, even if not wholeheartedly, but evidently not Rykard.
Theorizing on the Shaded Castle originally having been vassal to the Manor was popular when the Shaded Castle still appeared important, the obvious connections for this being the castle's purpose and the Champion's Song painting.
Namely, the castle's lords are storied executioners, and the painting leads to the Harp Bow reward, which seems to directly reference Rykard:
Bow fashioned from a minstrel's harp. Sonorous tones still resound when firing arrows.
Troubadours sing tales of champions, both in the honorable service of the Erdtree, and the one who spurns honor for blasphemy.
Even the Distinguished Greatshield, though it may more accurately be the lost Gelmir Knight Shield, could act as connective tissue for this idea, being that the sons of House Marais were born sickly and the shield emblematic of great families' timid children (and of Rykard-esque symbology).
Most clear to most though, is simply position:
On the balance of things, the Castle appears like it would have been managed by the Manor, as opposed to Leyndell all the way across the Altus. As I recall, Maleigh Marais and the dead overseer outside the Blade of Calling's room wear the Ruler's Robe, while Rya wears the green robes under the Ruler's Robe, further suggesting their assocation.
And yet, this castle is under the Cleanrots' protection, even to the point of having Cleanrot commanders (Halo Scythe):
I think a nice story can be established, if the green glintstone on the Cleanrot Spears is given function.
Indeed, there could be one, being the "power-source" for the Cleanrot Spears' diminutive shields' protective incantation warding against rot.
There appear to be 2 incantations upon the spear, one for the AoW and one for the rot-protection.
Spear:
Spear of the Cleanrot Knights who fought alongside Malenia, Blade of Miquella.
The winged golden blade deals holy damage. The diminutive shield is blessed with an incantation that wards off rot.
Sacred Phalanx (AoW):
Release the power of a hidden incantation to erect a palisade of golden spears frontwards.
The actuation of the "hidden incantation" does not seem to especially involve the shield or glintstone, as neither lights up; only the spear head lights up, with a golden glow, and this is maintained throughout the spear animation:
Namely, there is the hidden incantation placed upon the golden spear head, involving the spectral production of spears (like Messmer's Assualt, but I digress), and a separate incantation involving the shield and it protecting against rot.
It should be noted that the shield is still functioning; immunity increases by 50 with the spear (poison, deadly poison, rot).
With other incantations placed upon items, like the protective incantation of the Tree Sentinels' shields, our FP is required to activate the incantation; items passively giving benefits to the player are not rare, but I find it a bit hard to believe that each and every spear was given a strong enough incantation to last the eons.
It is also dubious as to whether Miquella had a master smith or troll smith (like Iji) who could smith innately rot-resistant weapons, but regardless, there is another piece of evidence, albeit minimal, that could suggest the green glintstone and shield are producing the rot-resistance.
Namely, Radahn's Spears, colored by both rot and probably Radahn's blood, lack both the glintstones and the shields. The holes for the glintstones are faintly modelled, so presumably leaving out the glintstones was intentional:
just behind spear head, no gems
For sake of testing, they also do not appear when fired by Radahn's bow's AoW:
Now, obviously, they are sized down and will lose details because of this. To me, however, it is enough that a spear designed to resist rot became rotted after losing its shield and gems.
Thus, I would attribute the function of the gems to be something of a power source for the shields' incantation, or an additional implement reducing the rot sustained by the spear, based on the poison association.
The association between poison and rot are well established, so I won't rehash them here.
Moving on, though, I think a satisfying story can be established.
Namely, the Shaded Castle, as vassal to the Manor, was an additional location for executions to take place, and also an area where poison arts were developed, for the benefits of the Manor's Inquisitors and assassins. Perhaps the 2 mines were in the possession of the Manor, or they were managed by the castle, but either way, by the time Malenia started gearing up for war, there was a need for rot-resistant techniques accessible to the common knights; not everybody had a pocket Miquella to consecrate their weapons. Thus, Malenia identified both a source for green glintstone, which could be used to modulate the effects of rot, and a devoted follower who would produce the Cleanrots' armor, in Maleigh Marais. He would betray Rykard, and choose to stand with Malenia. As such, the Stranded spirit NPC would refer to House Marais' later ruin as "just deserts", for aligning with Malenia, and even Cleanrot commanders would remain in the Shaded Castle, as a strategic key site for the ensuing march to Radahn. Though, after Malenia's bloom, with Radahn rotting, the Haligtree ruined, and Elemer rampaging, the Cleanrots appear to have been abandoned here, left protecting a deposed ally's domain.
tldr: Malenia gave a simp her old arm in exchange for billions in gems
Source: r/EldenRingLoreTalk · by /u/GwynsenKnight